The present invention is related to WDM (Wavelength Division Multiplexing) optical systems and, more particularly, to switching architectures of nodes for handling optical channels in WDM network systems.
WDM refers to network systems in which multiple optical signals having different wavelengths can share an optical fiber, each wavelength defining a particular communication channel. In a stricter sense, WDM also refers to an ITU (International Telecommunications Union) standard which includes the specification of the particular channel wavelengths and the spacings between these channels. DWDM (Dense WDM) refers to a more recent ITU standard in which the channel spacings are tighter so that more wavelength channels can be packed into an optical fiber. It should be noted that the term WDM, as used herein, refers to the first, more inclusive sense so as to include the ITU WDM and DWDM standards, unless specifically stated otherwise.
WDM has many advantages for optical communication systems including increased capacity. A representative WDM network may include many nodes connected to one another by optical fibers in a mesh or in a ring arrangement. At each node typically, only a portion of the wavelengths (also referred to as WDM channels) are used for transmission and reception, while the other wavelengths remain untouched as “pass-through” channels. For reception, a node isolates and removes (or “drops”) these particular channel signals from the light flow in an optical fiber for processing by receiver circuitry within the node or for otherwise rerouting the signals; for transmission, the node generates or routes (or “adds”) particular channel signals generated elsewhere into the light flow in an optical fiber for transmission to designated destinations over the network. Besides these add and drop functions, many nodes have switching functions by which signals in one channel carried in one optical fiber are switched to a different fiber, by which signals in one wavelength channel are switched to a different wavelength channel, or by which signals in a wavelength channel are switched to a different optical fiber in a different wavelength channel.
Heretofore, switching architectures for such nodes have been directed toward achieving full functionality with resulting high costs. This has impeded the adoption of optical networks and the advantages of large bandwidth in telecommunication networks. Alternatively, some switching architectures with low costs have been advocated, but with limited functions and utility.
Based upon newly emerging technologies, the present invention provides for switching architectures for nodes in which different functional levels are separated by interfaces. This allows each level to be constructed and treated as a module. This construction allows node repairs to be made easily. Furthermore, the node can be upgraded easily and systematically with sufficient functionalities to provide the desired utility to the user, i.e., the node has the desired functions on an “as-needed” basis. Costs are contained to encourage the adoption of optical networks.